a) Field of the Invention
The invention is directed to a coordinate measurement device with a base frame, a measurement table supported at the latter for holding an object to be measured, a sensing device for sensing the surface of the object to be measured, and with a positioning device for moving the sensing device in three spatial axes over the measurement table, which positioning device is mounted at the base frame and carries the sensing device.
b) Description of the Related Art
Coordinate measurement devices of the type mentioned above are used for sensing the shape of an object to be measured and for accurately measuring this object. Apart from first-time determination of the geometric data of such an object, coordinate measurement devices can also be used to check the dimensional stability of objects in a manufacturing line.
Coordinate measurement devices are high-precision instruments whose measuring accuracy exceeds that of the manufacturing equipment utilized for producing the object to be measured. In contrast to manufacturing devices, however, the forces occurring during a sensing process remain small.
For sensing larger objects, the prior art discloses coordinate measurement devices in portal-type construction in which the sensing device is arranged at a vertically displaceable spindle sleeve which is mounted at a crosspiece arranged between the two portal columns so as to be displaceable along this crosspiece. Together, the columns with the crosspiece form a portal which spans a measurement table and is movable along the same in air bearings. Due to the portal straddling the measurement table, this known construction provides good structural rigidity, but is relatively uneconomical and needs considerable space. In addition, free access to the measurement table is restricted by the portal-type construction and, with heavy workpieces, the orientation of the precision guides is influenced by the occurring introduction of forces, which results in inaccurate measurements.
In order to meet the requirements for high measuring accuracy, high-precision bearings, usually in the form of air bearings, have been used heretofore in coordinate metrology. A high degree of purity of the surrounding atmosphere and a temperature level that is as constant is possible are required for air bearings, so that these coordinate measurement devices must be operated in special rooms and can not be set up in the immediate vicinity of manufacturing equipment.
It is the primary object of the invention to provide a coordinate measurement device which is capable of working with high accuracy and in a highly dynamic manner and which also permits use in the immediate vicinity of manufacturing.
This object is met by a coordinate measurement device of the type mentioned above in which the positioning device has a first slide which is guided at the base frame in a first direction and which is movable on one side of the measurement table toward and away from the latter and on which a second slide is movable in a second direction vertical to the first direction, this second slide being provided at its end area remote of the measurement tablexe2x80x94considered in its movement directionxe2x80x94with a supporting portion which projects lateral to the measurement table and at which there is arranged a U-arm or stirrup arm which projects over the measurement table in a direction vertical to a principal work plane of the measurement table and which carries the sensing device at its free end over the measurement table and is constructed as an element that is rigid per se, wherein the first slide and the front area of the second slide situated in front of the supporting portion considered in the movement direction of the first slide can be moved in under the measurement table during the movement of the positioning device toward the measurement table.
Owing to the rigid construction of the stirrup arm and the consequent absence of any guides at the latter, it is possible to construct the stirrup arm in virtually any desired manner without restriction andxe2x80x94in contrast to a surrounding portal at which the sensing device is arranged so as to be movablexe2x80x94there is also no troublesome location-dependent bending of the stirrup arm (depending on its position relative to the measurement table). In cooperation with the supporting portion arranged laterally next to the measurement table, a superior accessibility to the entire surface of the measurement table over which the sensing device can be guided is achieved with the coordinate measurement device according to the invention.
Due to the fact that the stirrup arm used in the arrangement according to the invention has a substantially smaller mass than a portal extending around the measurement table, the coordinate measurement device according to the invention also works with appreciably increased dynamics of the entire system compared to the latter with respect to both principal and secondary processes. In addition, there is a wide variety of possible installation positions of the sensor (vertical, horizontal or other defined position). Moreover, relatively large bearing bases can be provided for the moving parts, which likewise benefits the measuring accuracy and structural rigidity of the device according to the invention.
A particularly compact construction results in that part of the positioning device can be moved under the measurement table. This allows the positioning device to be constructed with a wide, stable base and, accordingly, high rigidity, which again results in high measuring accuracy. When completely moved in, the supporting portion preferably comes into contact with a side edge of the measurement table. Since the supporting action relative to the base frame is caused for the most part by elements which are movable under the table, the supporting area on the side of the supporting portion remote of the measurement table can be relatively narrow and, therefore, particularly the area of the base frame next to the measurement table can also be kept compact with respect to dimensions so that the total setup surface needed for the coordinate measurement device is kept small.
Because of the relatively small mass of the positioning device (compared to a portal construction), the required acceleration forces and retardation forces for feeding the sensing device are also small. This results in a high positioning speed and therefore in heightened dynamics of the coordinate measurement device according to the invention.
Further, the very extensive freedom with regard to the shaping of the stirrup arm makes it possible to optimize the latter with respect to geometry and selection of material while taking into account the forces and moments occurring in a sensing process.
A particularly compact construction for the positioning device is preferably provided in that the stirrup arm is guided at the side of the supporting portion of the second slide facing away from the measurement table. In addition, the guide rails for the movement of the two slides relative to the measurement table can also be kept relatively short in this way, since the installation space needed for the guides of the stirrup arm does not occur as an idle path at these guide rails.
In an advantageous construction of the coordinate measurement device, the bearing support of the stirrup arm at the supporting portion is located approximately at the height of the sensing device provided at the free end of the stirrup arm. Accordingly, tilting moments occurring at the guides of the stirrup arm during a sensing process can be kept small so that measuring accuracy is improved.
The second slide preferably forms a substantially L-shaped section which is formed by the supporting portion extending substantially vertical to a principal work plane of the measurement table and is provided with guide devices for displaceable bearing support of the stirrup arm and by the front portion of the second slide, which front portion is connected with the supporting portion and extends essentially parallel to this principal work plane of the measurement table and is movable under the measurement table. On the one hand, this makes it possible to advance the second slide particularly close to the measurement table so that the stirrup arm can be kept short and, on the other hand, a stable support is achieved in the immediate vicinity of the workpiece to be measured.
The displaceable parts are preferably mounted by means of recirculating ball shoes or saddles on roller bearing-mounted section rail guides.
In order to improve guidance accuracy, the guide devices for the two slides and/or stirrup arm preferably comprise, respectively, two guide rails which are at a distance from one another and parallel to one another. This type of guidance is more robust than the high-precision air bearings used formerly and has good running accuracy. A drive device is preferably associated with the guide rails and is situated centrally therebetween so that there is a uniform introduction of force when the sensing device is advanced, and quantities interfering with the measurements as a result of the drive can be eliminated to a great extent.
In another advantageous construction of the invention, a coupling device is provided at the first slide at the end of the latter located in front with reference to its displacement direction; this coupling device is provided for temporarily coupling an object to be fed to the measurement table or a transport device for such an object, wherein the object or transport device can be drawn toward or onto the measurement table. This is particularly advantageous when the coordinate measurement device is operated in cooperation with an automatic or semi-automatic charging device, since the slide can then simultaneously cooperate in taking over the feed function for advancing the transport device or measured object to the measurement table, so that an independent feed device with separate drive and linked control can be dispensed with.
In another advantageous construction of the coordinate measurement device according to the invention, the stirrup arm mounted on the side of the supporting portion remote of the measurement table engages the supporting portion in such a way that it embraces or encircles it either on top or laterally in the direction of the measurement table.
In another advantageous construction of the invention, the stirrup arm is also mounted so as to be rotatable relative to the second slide, particularly about an axis of rotation parallel to the first direction (Y), so that curved lines or surfaces in particular can be sensed particularly easily.
In order to improve sensing of heavily fissured surface contours as well, the stirrup arm preferably comprises a cantilever arm which extends essentially parallel to the principal work plane of the measurement table and, adjoining the cantilever arm, an arm or stirrup which extends essentially vertical to the principal work plane and which carries, at its end, the sensing device.
In another advantageous embodiment of the invention, the sensing device is constructed as an exchangeable module which, as an add-on unit, can be coupled to and uncoupled from an interface of the stirrup arm designed for coupling different sensing devices. The coordinate measurement device can accordingly be adapted quickly and simply to different measuring tasks. The different sensing devices can be accommodated, for example, in a magazine in the movement area of the free end of the stirrup arm, for example, at an edge of the measurement table in suitable receptacles provided therein, so that sensing devices in the coordinate measurement device can even be exchanged automatically.
Lines are preferably arranged inside the stirrup arm for transmitting signals generated in the sensing device and are accordingly reliably protected from damage and from electromagnetic influences.
In the following, the invention will be explained more fully in principle with reference to the drawings.